The present disclosure relates generally to the field of motor vehicle brake systems. Specifically, a method and an electrohydraulic actuating assembly, for boosting the brake force in the case of such a brake system, are described.
In the case of an electrohydraulic brake system, the braking intention of a driver is usually sensed by means of a sensor in the region of a brake pedal and converted into an electrical signal. The electrical signal is supplied to a control unit, which then, on the basis of the signal, controls an electrical brake-pressure generator having an electromechanical actuator for generating brake force or assisting brake force.
Such a brake system is referred to as a “brake-by-wire” system if the brake force is generated exclusively by the electrical brake-pressure generator. By contrast, if the brake force generated by the driver is merely increased by means of the electrical brake-pressure generator, the term electrohydraulic brake force boost is used.
In order that the vehicle can still be decelerated even in the event of a defect or failure of the vehicle electrics, a “brake-by-wire” system normally has a redundant hydraulic emergency braking functionality (cf. DE 10 2004 016 141 A1). In this case, in a fallback mode, the actuating force generated on the brake pedal by the driver is transmitted directly to a brake master cylinder of the brake system by means of a mechanical push-through. In this way, a direct connection is produced between the brake pedal and the wheel brakes of the motor vehicle. Owing to the mechanical push-through the fallback mode is also referred to as “push-through” operation.
In the fallback mode of a “brake-by-wire” system, there is no control of the electrical brake-pressure generator. The deceleration of the vehicle must therefore be effected solely by means of the (unboosted) actuating force on the brake pedal. In the case of heavy vehicles, in particular, this results in excessively long braking distances.
In practice, it has been found that even a simple error of the sensor for detection of a braking request can result in deactivation of the electrical brake pressure generator. Although the electrical brake pressure generator as such would therefore still be able to operate, in these cases the vehicle has to be braked solely by the actuating force on the brake pedal. This applies both to “brake-by-wire” systems and to electrohydraulic brake force boosting systems with permanent mechanical push-through.